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Reasons for calcination

Release time:2019-11-09 From: Zhengnai Industry in China

Definition of calcination

The high-temperature heat treatment of various solid carbonaceous raw materials under air-insulated conditions is called calcination. Calcination is an important process in the production of carbon products, and the physical and chemical properties of the raw materials are significantly improved after calcination.

There are four main points for calcination purposes.

  • 1. Exclude volatiles from the raw materials.
  • 2. Improve the density and mechanical strength of carbonaceous materials.
  • 3. Improve the electrical conductivity of the raw materials.
  • 4. Improve the chemical stability of raw materials.

Excluding raw material volatiles is the primary condition

Eliminating the volatiles in the raw materials is the primary condition for improving the physical and chemical properties of the raw materials.

Carbonaceous raw material volume shrinkage results

At the same time that the carbonaceous raw material continuously discharges volatile matter during the high-temperature heat treatment, the molecular structure changes, the volume of the coke block shrinks, and the volume shrinkage results in the density and mechanical strength of the raw material.

Reasons for improved conductivity of raw materials

The improvement in the electrical conductivity of the raw material is a combined effect of the emission of volatiles and the increase in true density upon calcination. The higher the true density of the carbonaceous material after calcination, the lower the resistivity.

Calcination can improve the chemical stability of raw materials

The raw materials discharge a large amount of volatiles during the calcination process, increase the density, reduce the porosity, and also improve the oxidation resistance and chemical stability of the raw materials.

Moisture content is one of the analyzed items

The moisture content of the raw materials after calcination is also one of the frequently analyzed items, although reducing moisture is not the main purpose of calcination.

Size of graphite electrode

Item Unit RP HP UHP
300-500mm 300-500mm 300-500mm
Electric resistivity Electrode μΩm 7.5-8.6 5.5-6.8 4.6-6.2
Nipple 4.5-6.0 4.0-5.5 3.5-5.0
Bending strength Electrode Mpa ≥7.5 ≥10.0 ≥10.5
Nipple ≥16.0 ≥18.0 ≥20.0
Elastic modulus Electrode Gpa ≤9.0 ≤13.0 ≤14.0
Nipple ≤13.0 ≤15.0 ≤20.0
Bulk density Electrode g/cm3 1.54-1.62 1.62-1.70 1.66-1.73
Nipple 1.70-1.78 1.72-1.80 1.75-1.82
CTE(100-600℃) Electrode 10-6/℃ 2.20-2.60 1.80-2.20 1.20-1.50
Nipple 1.50-1.90 1.50-1.80 1.10-1.40
Ash % ≤0.3 ≤0.3 ≤0.3